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Isolation, Identification, and Pathogenicity of Fusarium spp. from Guayule in Arizona. Ronald E. Ykema, Former Graduate Research Assistant, Department of Botany, Arizona State University, Tempe 85287-1601. Jean C. Stutz, Associate Professor, Department of Botany, Arizona State University, Tempe 85287-1601. Plant Dis. 75:736-738. Accepted for publication 29 January 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0736.

Fusarium equiseti, F. oxysporum, and F. solani were isolated from necrotic root tissue of diseased guayule plants. F. solani was the most prevalent of the three species isolated. The pathogenicity of 22 isolates was tested using the slant board nutrient solution technique. Although isolates of all species caused root rot symptoms, some isolates of F. oxysporum were the most virulent, causing root rot symptoms in 6070% of the roots inoculated. In additional tests for pathogenicity, greenhouse-grown plants were inoculated with spore suspensions of Fusarium spp. Isolates of F. oxysporum discolored lateral roots and taproots and reduced fresh weights. Isolates of F. oxysporum directly penetrated and colonized roots and formed distributive hyphae in the root cortex.

Keyword(s): Parthenium argentatum.